Nunjucks autoescape bypass leads to cross site scriptingGHSA-x77j-w7wf-fjmw
MEDIUMFix: mozilla/nunjucks#1437GHSA-x77j-w7wf-fjmw is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in nunjucks. A fix is available for nunjucks — see the affected versions and patch details below.
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for GHSA-x77j-w7wf-fjmw.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
nunjucksnpmDescription
Impact
In Nunjucks versions prior to version 3.2.4, it was possible to bypass the restrictions which are provided by the autoescape functionality. If there are two user-controlled parameters on the same line used in the views, it was possible to inject cross site scripting payloads using the backslash \ character.
Example
If the user-controlled parameters were used in the views similar to the following:
<script>
let testObject = { lang: '{{ lang }}', place: '{{ place }}' };
</script>
It is possible to inject XSS payload using the below parameters:
https://<application-url>/?lang=jp\&place=};alert(document.domain)//
Patches
The issue was patched in version 3.2.4.
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | nunjucks | all versions | 3.2.4npm install nunjucks@3.2.4 |
Affected Products
nunjucksmozillaDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nunjucks, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nunjucks to 3.2.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-x77j-w7wf-fjmw is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is GHSA-x77j-w7wf-fjmw in your dependencies?
Find it across npm, including transitive dependencies.